FIG. 11 is a sectional view of the flow path of a conventional ultrasonic flowmeter. In FIG. 11, flow path 30 having a rectangular cross section is divided into multiple paths along opposing long sides of flow path 30 by multiple partition plates 31 to form multilayer flow path 32. Multilayer flow path 32 has approach flow paths 33, 34 linked thereto at upstream and downstream thereof.
Upstream chamber 35 and downstream chamber 36 forming a U shape together with flow path 30 allow each front end of approach flow paths 33, 34 to be positioned in a projecting state. Turnback plates 37, 38 are provided to regulate a flow. Regulating material 39 made of a porous material is provided to regulate a flow in multilayer flow path 32.
An ultrasonic transducer (not illustrated) is a means for sending and receiving ultrasonic waves. Ultrasonic transducers are provided at the opposing short sides of flow path 30 so that ultrasonic waves obliquely cross the flow direction of a fluid across flow path 30 at a certain angle with respect to the page surface.
Such a ultrasonic flowmeter calculates flow velocity on different occasions according to propagation time of ultrasonic waves sent and received by a pair of ultrasonic transducers; and multiplies the flow velocity by such as the cross-sectional area of the flow path as required to compute a flow rate (refer to patent literature 1 for instance).
With the configuration of a conventional ultrasonic flowmeter, however, a bend of the flow path and a local change of the cross-sectional area of flow path 30 cause an uneven flow at the bent part. When a measured fluid flows from the upstream side to the measuring part, vertically uneven flows are generated near the inlet of the measuring part, thereby preventing the fluid from evenly flowing into each layer.
This makes it difficult to measure the flow rate of the entire flow path using ultrasonic waves; and shows influence of the flow velocity distribution, resulting in different measuring precisions depending on flow velocity.
To increase the measuring precision of the ultrasonic flowmeter, additional components for flow regulation are required, thereby complicating the structure of the ultrasonic flowmeter. In mass-producing ultrasonic flowmeters, such components require additional worker-hours for example, which increases the production cost.
[Patent literature 1] Japanese Patent Unexamined Publication No. 2004-132928